Polyvinyl alcohol films prepared by coating methods

ABSTRACT

A method of film fabrication is taught that uses a coating and drying apparatus to fabricate resin films suitable for optical applications. In particular, polyvinyl alcohol films are prepared by simultaneous application of multiple liquid layers to a moving carrier substrate. After solvent removal, the polyvinyl alcohol films are peeled from the sacrificial carrier substrate. Polyvinyl alcohol films prepared by the current invention exhibit good dimensional stability and low birefringence.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a 111A Application of Provisional Application Serial No.60/381,931, filed on May 20, 2002

FIELD OF THE INVENTION

[0002] This invention relates generally to methods for manufacturingresin films and, more particularly, to an improved method formanufacturing optical films, and most particularly to the manufacture ofpolyvinyl alcohol films used to fabricate light polarizers suitable forthe preparation of optical media such as sunglasses, light filters,liquid crystal displays and other electronic displays.

BACKGROUND OF THE INVENTION

[0003] Polyvinyl alcohol films are used to form light polarizers.Practical applications of light polarizers include filters for opticallenses of cameras, microscopes and sunglasses. Polarizers are also usedin the screens of cathode ray tube displays to reduce glare. Morerecently, polarizers have been utilized in liquid crystal displays, OLED(organic light emitting diode) displays, and in other electronicdisplays used in, for example, personal computers, televisions, cellphones, and instrument panels.

[0004] The materials and methods used to prepare light polarizers fromresin films of the polyvinyl alcohol type are well known in the art asoriginally described in U.S. Pat. No. 2,237,567 to Land. A practicaldiscussion of the manufacturing process for polarizers using polyvinylalcohol films and staining dyes may be found in U.S. Pat. No. 4,591,512to Racich. Briefly, an amorphous film of polyvinyl alcohol is stretchedand dyed with iodine. By orienting the polymers in the film duringstretching, the light absorbing iodine dye is also oriented, and thefilm becomes dichroic. When light waves pass through a dichroicmaterial, many of the light waves with a particular vibration directionare absorbed. The emerging light predominately vibrates in only onedirection and is described as plane polarized light or linearlypolarized light.

[0005] There have been a number of improvements upon the materials andmethods originally taught in U.S. Pat. No. 2,237,567 to Land. Forexample, the finished polyvinyl alcohol film may be dimensionallystabilized with respect to temperature and humidity by treatment withboric acid as taught by U.S. Pat. No. 2,445,555 to Binda or by treatmentwith organosilanes as disclosed in U.S. Pat. No. 4,818,624 to Downey.Alternatively, light polarizers may be prepared without staining withdyes. For example, the polyvinyl alcohol film may be treated withhydrochloric acid at high temperature to create polyvinylene segmentswithin the film, and this treatment imparts dichroic properties to thesheet as taught by U.S. Pat. No. 2,173,304 to Land. In U.S. Pat. No.5,973,834 to Kadaba, streak and mottle artifacts sometimes found duringfabrication of polyvinylene sheets are claimed to be minimized bybonding or laminating the polyvinyl alcohol film to a support prior toacid treatment.

[0006] Regardless of the methods used to prepare light polarizers,amorphous polyvinyl alcohol sheets are used almost exclusively as theprecursor film. Polyvinyl alcohol having a high degree of hydrolysis(i.e. greater than 98% saponified) is preferred. Other hydroxylatedpolymers, such as, polyvinylacetals, polyvinylketals and cellulosics, aswell as polyesters, have been mentioned as potential substitutes, butpolyvinyl alcohol is generally preferred due to the well knownproperties and ready availability of this material (see backgrounddiscussions in U.S. Pat. No. 4,895,769 to Land or U.S. Pat. No.5,925,769 to Connolly.

[0007] In general, resin films are prepared either by melt extrusionmethods or by casting methods. Melt extrusion methods involve heatingthe resin until molten (approximate viscosity on the order of 100,000cp), and then applying the hot molten polymer to a highly polished metalband or drum with an extrusion die, cooling the film, and finallypeeling the film from the metal support. For many reasons, however,films prepared by melt extrusion are generally not suitable for opticalapplications. Principal among these is the fact that melt extruded filmsexhibit a high degree of optical birefringence. In the case of highlyhydrolyzed polyvinyl alcohol, there is the additional problem of meltingthe polymer. Highly saponified polyvinyl alcohol has a very high meltingtemperature of 230° C., and this is above the temperature wherediscoloration or decomposition begins (˜200° C.). For these reasons,melt extrusion methods are not practical for fabricating many resinfilms including the highly hydrolyzed polyvinyl alcohol films used toprepare light polarizers. Rather, casting methods are generally used tomanufacture these films.

[0008] Resin films for optical applications are manufactured almostexclusively by casting methods. Casting methods involve first dissolvingthe polymer in an appropriate solvent to form a dope having a highviscosity on the order of 50,000 cp, and then applying the viscous dopeto a continuous highly polished metal band or drum through an extrusiondie, partially drying the wet film, peeling the partially dried filmfrom the metal support, and conveying the partially dried film throughan oven to more completely remove solvent from the film. Cast filmstypically have a final dry thickness in the range of 40-200 μm. Ingeneral, thin films of less than 40 μm are very difficult to produce bycasting methods due to the fragility of wet film during the peeling anddrying processes. Films having a thickness of greater than 200 μm arealso problematic to manufacture due to difficulties associated with theremoval of solvent in the final drying step. Although the dissolutionand drying steps of the casting method add complexity and expense, castfilms generally have better optical properties when compared to filmsprepared by melt extrusion methods, and problems associated withdecomposition at high temperature are avoided.

[0009] Examples of optical films prepared by casting methods include:1.) Polyvinyl alcohol sheets used to prepare light polarizers asdisclosed in U.S. Pat. No. 4,895,769 to Land and U.S. Pat. No. 5,925,289to Cael as well as more recent disclosures in U.S. Patent ApplicationSerial No. 2001/0039319 A1 to Harita and U.S. Patent Application. SerialNo. 2002/001700 A1 to Sanefuji, 2.) Cellulose triacetate sheets used forprotective covers for light polarizers as disclosed in U.S. Pat. No.5,695,694 to Iwata, 3.) Polycarbonate sheets used for protective coversfor light polarizers or for retardation plates as disclosed in U.S. Pat.No. 5,818,559 to Yoshida and U.S. Pat. Nos. 5,478,518 and 5,561,180 bothto Taketani, and 4.) Polysulfone sheets used for protective covers forlight polarizers or for retardation plates as disclosed in U.S. Pat.Nos. 5,759,449 and 5,958,305 both to Shiro.

[0010] Despite the wide use of the casting method to manufacture opticalfilms, however, there are a number of disadvantages to castingtechnology. One disadvantage is that cast films have significant opticalbirefringence. Although films prepared by casting methods have lowerbirefringence when compared to films prepared by melt extrusion methods,birefringence remains objectionably high. For example, cellulosetriacetate films prepared by casting methods exhibit in-planeretardation of 7 nanometers (nm) for light in the visible spectrum asdisclosed in U.S. Pat. No. 5,695,694 to Iwata. Polycarbonate filmsprepared by casting methods exhibit in-plane retardation of 17 nm asdisclosed in U.S. Pat. Nos. 5,478,518 and 5,561,180 both to Taketani.U.S. Patent Applic. Ser. No. 2001/0039319 A1 to Harita suggests thatcolor irregularities in stretched polyvinyl alcohol sheets are reducedwhen the difference in retardation between widthwise positions withinthe film is less than 5 nm in the original unstretched film. Thus, lowin-plane birefringence is desirable for polyvinyl alcohol films used toprepare polarizers. For many applications of optical films, low in-planeretardation values are desirable. In particular, values of in-planeretardation of less than 10 nm are preferred.

[0011] Birefringence in cast films arises from orientation of polymersduring the manufacturing operations. This molecular orientation causesindices of refraction within the plane of the film to be measurablydifferent. In-plane birefringence is the difference between theseindices of refraction in perpendicular directions within the plane ofthe film. The absolute value of birefringence multiplied by the filmthickness is defined as in-plane retardation. Therefore, in-planeretardation is a measure of molecular anisotropy within the plane of thefilm.

[0012] During the casting process, molecular orientation may arise froma number of sources including shear of the dope in the die, shear of thedope by the metal support during application, shear of the partiallydried film during the peeling step, and shear of the free-standing filmduring conveyance through the final drying step. These shear forcesorient the polymer molecules and ultimately give rise to undesirablyhigh birefringence or retardation values. To minimize shear and obtainthe lowest birefringence films, casting processes are typically operatedat very low line speeds of 1-15 m/min as disclosed in U.S. Pat. No.5,695,694 to Iwata. Slower line speeds generally produce the highestquality films.

[0013] Another drawback to the casting method is the inability toaccurately apply multiple layers. As noted in U.S. Pat. No. 5,256,357 toHayward, conventional multi-slot casting dies create unacceptablynon-uniform films. In particular, line and streak non-uniformity isgreater than 5% with prior art devices. Acceptable two layer films maybe prepared by employing special die lip designs as taught in U.S. Pat.No. 5,256,357 to Hayward, but the die designs are complex and may beimpractical for applying more than two layers simultaneously.

[0014] Another drawback to the casting method is the restrictions on theviscosity of the dope. In casting practice, the viscosity of dope is onthe order of 50,000 cp. For example, U.S. Pat. No. 5,256,357 to Haywarddescribes practical casting examples using dopes with a viscosity of100,000 cp. In general, cast films prepared with lower viscosity dopesare known to produce non-uniform films as noted for example in U.S. Pat.No. 5,695,694 to Iwata. In U.S. Pat. No. 5,695,694 to Iwata, the lowestviscosity dopes used to prepare casting samples are approximately 10,000cp. At these high viscosity values, however, casting dopes are difficultto filter and degas. While fibers and larger debris may be removed,softer materials such as polymer slugs are more difficult to filter atthe high pressures found in dope delivery systems. Particulate andbubble artifacts create conspicuous inclusion defects as well as streaksresulting in substantial waste.

[0015] In addition, prior art casting methods can be relativelyinflexible with respect to product changes. Because casting requireshigh viscosity dopes, changing product formulations requires extensivedown time for cleaning delivery systems to eliminate the possibility ofcontamination. Particularly problematic are formulation changesinvolving incompatible polymers and solvents. In fact, formulationchanges are so time consuming and expensive with prior art castingmethods that most production machines are dedicated exclusively toproducing only one film type.

[0016] Finally, cast films may exhibit undesirable cockle or wrinkles.Thinner films are especially vulnerable to dimensional artifacts eitherduring the peeling and drying steps of the casting process or duringsubsequent handling of the film. In particular, the preparation ofcomposite optical plates from resin films requires a lamination processinvolving application of adhesives, pressure, and high temperatures.Very thin films are difficult to handle during this lamination processwithout wrinkling. In addition, many cast films may naturally becomedistorted over time due to the effects of moisture. This phenomenon mayoccur in free-standing films or in rolls of film, and is particularlyproblematic for films made from moisture sensitive resins such aspolyvinyl alcohol. For optical films, good dimensional stability isnecessary during storage as well as during subsequent fabrication ofcomposite optical plates.

SUMMARY OF THE INVENTION

[0017] It is therefore an object of the present invention to overcomethe limitations of prior art casting methods and provide a new coatingmethod for preparing amorphous polyvinyl alcohol films having very lowin-plane birefringence.

[0018] It is a further object of the present invention to provide a newmethod of producing highly uniform polyvinyl alcohol films over a broadrange of dry thicknesses.

[0019] Yet another object of the present invention is to provide amethod of preparing polyvinyl alcohol films by simultaneously applyingmultiple layers to a moving substrate.

[0020] Still another object of the present invention is to provide a newmethod of preparing polyvinyl alcohol films with improved dimensionalstability and handling ability by temporarily adhering the polyvinylalcohol film to a supporting carrier substrate at least until it issubstantially dry and then subsequently separating the carrier substratefrom the polyvinyl alcohol film.

[0021] Briefly stated, the foregoing and numerous other features,objects and advantages of the present invention will become readilyapparent upon review of the detailed description, claims and drawingsset forth herein. These features, objects and advantages areaccomplished by applying a low viscosity fluid containing polyvinylalcohol resin onto a moving carrier substrate by a coating method. Thepolyvinyl alcohol film is not separated from the carrier substrate untilthe coated film is substantially dry (<10% residual solvent by weight).In fact, the composite structure of polyvinyl alcohol film and carriersubstrate may be wound into rolls and stored until needed. Thus, thecarrier substrate cradles the polyvinyl alcohol film and protectsagainst shearing forces during conveyance through the drying process.Moreover, because the polyvinyl alcohol film is dry and solid when it isfinally peeled from the carrier substrate, there is no shear ororientation of polymer within the film due to the peeling process. As aresult, polyvinyl alcohol films prepared by the current invention areremarkably amorphous and exhibit very low in-plane birefringence.

[0022] Polyvinyl alcohol films can be made with the method of thepresent invention having a thickness in the range of from about 1 toabout 500 μm. Further, very thin polyvinyl alcohol films of less than 40μm can be easily manufactured with the method of the present inventionat line speeds not possible with prior art methods. The fabrication ofvery thin films is facilitated by a carrier substrate that supports thewet film through the drying process and eliminates the need to peel thefilm from a metal band or drum prior to a final drying step as requiredin the casting methods described in prior art. Rather, the polyvinylalcohol film is substantially, if not completely, dried beforeseparation from the carrier substrate. In all cases, dried PVA filmshave a residual solvent content of less than 10% by weight. Thus, thepresent invention readily allows for preparation of very delicate thinfilms not possible with the prior art casting method. In addition, thickfilms of greater than 40 μm may also be prepared by the method of thepresent invention. To fabricate thicker films, additional coatings maybe applied over a film-substrate composite either in a tandem operationor in an offline process without comprising optical quality. In thisway, the method of the present invention overcomes the limitation ofsolvent removal during the preparation of thicker films since the firstapplied film is dry before application of a subsequent wet film. Thus,the present invention allows for a broader range of final film thicknessthan is possible with casting methods.

[0023] In the method of the present invention, polyvinyl alcohol filmsare created by forming a single or, preferably, a multi-layer compositeon a slide surface of a coating hopper, the multi-layer compositeincluding a bottom layer of low viscosity, one or more intermediatelayers, and an optional top layer containing a surfactant, flowing themulti-layer composite down the slide surface and over a coating lip ofthe coating hopper, and applying the multi-layer composite to a movingsubstrate. In particular, the use of the method of the present inventionis shown to allow for application of several liquid layers having uniquecomposition. Coating aids and additives may be placed in specific layersto improve film performance or improve manufacturing robustness. Forexample, multi-layer application allows a surfactant to be placed in thetop spreading layer where needed rather than through out the entire wetfilm. In another example, the concentration of polyvinyl alcohol in thelowermost layer may be adjusted to achieve low viscosity and facilitatehigh-speed application of the multi-layer composite onto the carriersubstrate. Therefore, the present invention provides an advantageousmethod for the fabrication of multiple layer composite films such asrequired for certain optical elements or other similar elements.

[0024] Wrinkling and cockle artifacts are minimized with the method ofthe present invention through the use of the carrier substrate. Byproviding a stiff backing for the polyvinyl alcohol film, the carriersubstrate minimizes dimensional distortion of the polyvinyl alcoholfilm. This is particularly advantageous for handling and processing verythin films of less than about 40 microns. In addition, the restrainingnature of the carrier substrate also eliminates the tendency ofpolyvinyl alcohol films to distort or cockle over time as a result ofchanges in moisture levels. Thus, the method of the current inventioninsures that polyvinyl alcohol films are dimensionally stable duringpreparation and storage as well as during final handling steps necessaryfor fabrication of optical elements.

[0025] In the practice of the method of the present invention, it ispreferred that the substrate be a discontinuous sheet such aspolyethylene terephthalate (PET). The PET carrier substrate may bepretreated with a subbing layer or an electrical discharge device tomodify adhesion between the polyvinyl alcohol film and the PETsubstrate. In particular, a subbing layer or electrical dischargetreatment may enhance the adhesion between the film and the substrate,but still allow the film to be subsequently peeled away from thesubstrate.

[0026] Although the present invention is discussed herein withparticular reference to a slide bead coating operation, those skilled inthe art will understand that the present invention can be advantageouslypracticed with other coating operations. For example, freestanding filmshaving low in-plane retardation should be achievable single or multiplelayer slot die bead coating operations and single or multiple layercurtain coating operations. Moreover, those skilled in the art willrecognize that the present invention can be advantageously practicedwith alternative carrier substrates. For example, peeling films havinglow in-plane birefringence should be achievable with other resinsupports (e.g. polyethylene naphthalate (PEN), cellulose acetate,polycarbonate, PET), paper supports, resin laminated paper supports, andmetal supports (e.g. aluminum). Practical applications of the presentinvention include the preparation of polyvinyl alcohol sheets used foroptical films, polarizer films, laminate films, release films, andpackaging films among others. In particular, polyvinyl alcohol sheetsprepared by the method of the present invention may be utilized asoptical films in the manufacture of electronic displays such as liquidcrystal displays. For example, liquid crystal displays are comprised ofa number of film elements including polarizer plates, compensationplates and electrode substrates. Polarizer plates are typically amulti-layer composite structure having dichroic film (normally stretchedpolyvinyl alcohol treated with iodine) with each surface adhered to aprotective cover. The polyvinyl alcohol films prepared by the method ofthe present invention are suitable for the formation of polarizer films.The polyvinyl alcohol films prepared by the method of the presentinvention are also suitable for the manufacture of compensation plates.

[0027] The polyvinyl alcohol film produced with the method of thepresent invention is an optical film. As produced the polyvinyl alcoholfilm made with the method of the present invention will have a lighttransmittance of at least about 85 percent, preferably at least about 90percent, and most preferably, at least about 95 percent. Further, asproduced the polyvinyl alcohol film will have a haze value of less than1.0 percent. In addition, the polyvinyl alcohol films are smooth with asurface roughness average of less than 100 nm and most preferrably witha surface roughness of less than 50 nm

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a schematic of an exemplary coating and drying apparatusthat can be used in the practice of the method of the present invention.

[0029]FIG. 2 is a schematic of an exemplary coating and drying apparatusof FIG. 1 including a station where the polyvinyl alcohol web separatedfrom the substrate is separately wound.

[0030]FIG. 3 is a schematic of an exemplary multi-slot coating apparatusthat can be used in the practice of the method of the present invention.

[0031]FIG. 4 shows a cross-sectional representation of a single-layerPVA film partially peeled from a carrier substrate and formed by themethod of the present invention.

[0032]FIG. 5 shows a cross-sectional representation of a single-layerPVA film partially peeled from a carrier substrate and formed by themethod of the present invention wherein the carrier substrate has asubbing layer formed thereon.

[0033]FIG. 6 shows a cross-sectional representation of a multi-layer PVAfilm partially peeled from a carrier substrate and formed by the methodof the present invention.

[0034]FIG. 7 shows a cross-sectional representation of a multi-layer PVAfilm partially peeled from a carrier substrate and formed by the methodof the present invention wherein the carrier substrate has a subbinglayer formed thereon.

[0035]FIG. 8 is a schematic of a casting apparatus as used in prior artto cast PVA films.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Turning first to FIG. 1 there is shown a schematic of anexemplary and well known coating and drying system 10 suitable forpracticing the method of the present invention. The coating and dryingsystem 10 is typically used to apply very thin films to a movingsubstrate 12 and to subsequently remove solvent in a dryer 14. A singlecoating apparatus 16 is shown such that system 10 has only one coatingapplication point and only one dryer 14, but two or three (even as manyas six) additional coating application points with corresponding dryingsections are known in the fabrication of composite thin films. Theprocess of sequential application and drying is known in the art as atandem coating operation.

[0037] Coating and drying apparatus 10 includes an unwinding station 18to feed the moving substrate 12 around a back-up roller 20 where thecoating is applied by coating apparatus 16. The coated web 22 thenproceeds through the dryer 14. In the practice of the method of thepresent invention, the final dry film, 24 comprising a PVA film onsubstrate 12, is wound into rolls at a wind-up station 26.

[0038] As depicted, an exemplary four-layer coating is applied to movingweb 12. Coating liquid for each layer is held in respective coatingsupply vessel 28, 30, 32, 34. The coating liquid is delivered by pumps36, 38, 40, 42 from the coating supply vessels to the coating apparatus16 conduits 44, 46, 48, 50, respectively. In addition, coating anddrying system 10 may also include electrical discharge devices, such ascorona or glow discharge device 52, or polar charge assist device 54, tomodify the substrate 12 prior to application of the coating.

[0039] Turning next to FIG. 2 there is shown a schematic of the sameexemplary coating and drying system 10 depicted in FIG. 1 with analternative winding operation. Accordingly, the drawings are numberedidentically up to the winding operation. In the practice of the methodof the present invention the dry film 24 comprising a substrate (whichmay be a resin film, paper, resin coated paper or metal) with a PVAcoating applied thereto is taken between opposing rollers 56, 58. ThePVA film 60 is peeled from substrate 12 with the PVA film going towinding station 62 and the substrate 12 going to winding station 64. Ina preferred embodiment of the present invention, polyethylene phthalate(PET) is used as the substrate 12. The substrate 12 may be pretreatedwith a subbing layer to enhance adhesion of the coated film 60 to thesubstrate 12.

[0040] The coating apparatus 16 used to deliver coating fluids to themoving substrate 12 may be a multi-layer applicator such as a slide beadhopper, as taught for example in U.S. Pat. No. 2,761,791 to Russell, ora slide curtain hopper, as taught by U.S. Pat. No. 3,508,947 to Hughes.Alternatively, the coating apparatus 16 may be a single layerapplicator, such as slot die hopper, jet hopper, roller coating deviceor blade coating device. In a preferred embodiment of the presentinvention, the application device 16 is a multi-layer slide bead hopper.

[0041] As mentioned above, coating and drying system 10 includes a dryer14 which will typically be a drying oven to remove solvent from thecoated film. An exemplary dryer 14 used in the practice of the method ofthe present invention includes a first drying section 66 followed byeight additional drying sections 68-82 capable of independent control oftemperature and air flow. Although dryer 14 is shown as having nineindependent drying sections, drying ovens with fewer compartments arewell known and may be used to practice the method of the presentinvention. In a preferred embodiment of the present invention the dryer14 has at least two independent drying zones or sections.

[0042] Preferably, each of drying sections 66-82 has independenttemperature and airflow controls. In each section, temperature may beadjusted between 5° C. and 150° C. To minimize drying defects from casehardening or skinning-over of the wet polyvinyl alcohol film, slowdrying rates are needed in the early sections of dryer 14. Artifactscreated by premature case hardening include reticulation patterns orblistering of the polyvinyl alcohol film. In preferred embodiment of thepresent invention the first drying section 66 is operated at atemperature of at least about 5° C. but less than 50° C. with no directair impingement on the wet coating of the coated web 22. In anotherpreferred embodiment of the method of the present invention, dryingsections 68, 70 are also operated at a temperature of at least about 5°C. but less than 50° C. It is most preferred that initial dryingsections 66, 68 be operated at temperatures between about 10° C. andabout 40° C. The actual drying temperature in drying sections 66, 68 maybe optimized empirically within these ranges by those skilled in theart.

[0043] Referring now to FIG. 3, a schematic of an exemplary coatingapparatus 16 is shown in detail. Coating apparatus 16, schematicallyshown in side elevational cross-section, includes a front section 92, asecond section 94, a third section 96, a fourth section 98, and a backplate 100. There is an inlet 102 into second section 94 for supplyingcoating liquid to first metering slot 104 via pump 106 to thereby form alowermost layer 108. There is an inlet 110 into third section 96 forsupplying coating liquid to second metering slot 112 via pump 114 toform layer 116. There is an inlet 118 into fourth section 98 forsupplying coating liquid to metering slot 120 via pump 122 to form layer124. There is an inlet 126 into back plate 100 for supplying coatingliquid to metering slot 128 via pump 130 to form layer 132. Each slot104, 112, 120, 128 includes a transverse distribution cavity. Frontsection 92 includes an inclined slide surface 134, and a coating lip136. There is a second inclined slide surface 138 at the top of secondsection 94. There is a third inclined slide surface 140 at the top ofthird section 96. There is a fourth inclined slide surface 142 at thetop of fourth section 98. Back plate 100 extends above inclined slidesurface 142 to form a back land surface 144. Residing adjacent thecoating apparatus or hopper 16 is a coating backing roller 20 aboutwhich a web 12 is conveyed. Coating layers 108, 116, 124, 132 form amulti-layer composite which forms a coating bead 146 between lip 136 andsubstrate 12. Typically, the coating hopper 16 is movable from anon-coating position toward the coating backing roller 20 and into acoating position. Although coating apparatus 16 is shown as having fourmetering slots, coating dies having a larger number of metering slots(as many as nine or more) are well known and may be used to practice themethod of the present invention.

[0044] In the method of the current invention, the coating fluids arecomprised principally of polyvinyl alcohol dissolved in water. However,the coating fluids may also contain stabilizers, plasticizers,surfactants, and other addenda. In terms of stabilizers, compounds maybe added in small amounts to the coating fluids to minimize changes inviscosity during storage. Fluid stabilizing additives include alcohols,such as ethanol, isopropanol, n-propanol, isobutanol, n-butanol,cyclohexanol, and phenol, as well as thiocyanates, such as the calciumthiocyanate, sodium thiocyanate and ammonium thiocyante. The amount ofstabilizer added is preferably 0-10% by weight.

[0045] Appropriate plasticizers for polyvinyl alcohol films includepolyhydric alcohols such as glycerin and ethylene glycol as well asamine alcohols such as ethanolamine. Historically, plasticizers havebeen used to improve handling characteristics of polyvinyl alcohol filmsduring subsequent staining and stretching operations in the preparationof polarizers. In the method of the present invention, plasticizers mayalso be used as coating aids to minimize premature film solidificationat the coating hopper and to improve drying properties. However, the useof plasticizers is optional since there are applications forunplasticized polyvinyl alcohol films. In the method of the presentinvention, the amount of plasticizers added may be 0-30% by weightrelative to the amount of polyvinyl alcohol.

[0046] In the method of the present invention, surfactants are added ascoating aids to control artifacts arising from flow after coatingphenomena such as mottle, repellencies, orange peel (Bernard cells), andedge withdraw. Appropriate surfactants include those suitable foraqueous coating as described in numerous publications (see for exampleSurfactants: Static and dynamic surface tension by Y M Tricot in LiquidFilm Coating, pp 99-136, S E Kistler and P M Schweitzer editors, Chapmanand Hall [1997]). Surfactants may include nonionic, anionic, cationicand amphoteric types. Examples of practical surfactants includepolyoxyethylene ethers, such as polyoxyethylene (8) isooctylphenylether, polyoxyethylene (10) isooctylphenyl ether, and polyoxyethylene(40) isooctylphenyl ether, and fluorinated polyoxyethylene ethers suchas the Zonyl series commercially available from Du Pont. In the methodof the present invention, there are no particular limits as to the typeof surfactant used.

[0047] In terms of surfactant distribution, surfactants are onlynecessary in the uppermost layer of the multi-layer coating. In theuppermost layer, the concentration of surfactant is preferably0.001-1.000% by weight and most preferably 0.020-0.500%. Becausesurfactants are only necessary in the uppermost layer, the overallamount of surfactant remaining in the final dried film is small whencompared to the prior art method of casting. At these lower levels ofsurfactants, artifacts created by bleeding of the surfactant from thefinished polyvinyl alcohol film are greatly reduced. Artifacts createdby bleeding of surfactant include blocking of the polyvinyl alcohol filmand small viscous microscopic droplets that smear the film when handled.In the method of the present invention, a practical surfactantconcentration in the uppermost layer having a wet thickness of 10 μm is0.100% which after drying gives a final surfactant amount of 11 mg/sq-m.The coated film shows no evidence of bleeding. For casting, a surfactantconcentration of 0.050% through-out the entire wet film containing 20%PVA by weight is used to prevent sticking of the film to the metal drumor band. After drying, a finished film having a final dry thickness of48 μm contains surfactant in an amount of 155 mg/m². The cast filmdisplays conspicuous bleeding of surfactant. Thus, the method of thepresent invention not only reduces the amount of required surfactant bya factor of ten but also eliminates bleeding of the surfactant from thefinished film.

[0048] Turning next to FIGS. 4 through 7, there are presentedcross-sectional illustrations showing various film configurationsprepared by the method of the present invention. In FIG. 4, single-layerPVA film 150 is shown partially peeled from a carrier substrate 152. PVAfilm 150 may be formed either by applying a single liquid layer to thecarrier substrate 152 or by applying a multiple layer composite having acomposition that is substantially the same among the layers.Alternatively in FIG. 5, the carrier substrate 154 may have beenpretreated with a subbing layer 156 that modifies the adhesive forcebetween the single layer PVA film 158 and the substrate 154. FIG. 6illustrates a multiple layer film 160 that is comprised of fourcompositionally discrete layers including a lowermost layer 162, twointermediate layers 164, 166, and an uppermost layer 168, the lowermostlayer 162 being nearest to the carrier support 170. FIG. 6 also showsthat the entire multiple layer composite 160 may be peeled from thecarrier substrate 170. FIG. 7 shows a multiple layer composite film 172comprising a lowermost layer 174, two intermediate layers 176, 178, andan uppermost layer 180, the lowermost layer 174 being nearest to thecarrier substrate 182. The entire multiple-layer composite 172 is shownbeing peeled from the carrier substrate 182. The carrier substrate 182has been treated with a subbing layer 184 to modify the adhesion betweenthe composite film 172 and substrate 182. In a preferred embodiment ofthe present invention, the carrier substrate 182 is PET and the subbinglayer 184 contains a polymer of the vinylidene chloride type. Subbinglayer 184 may be comprised of other polymeric materials such aspolyvinylbutyrals, cellulosics, polyacrylates, and polycarbonates eitheralone or in conjunction with poly(acrylonitrile-co-vinylidenechloride-co-acrylic acid). The choice of materials used in the subbinglayer may be optimized empirically by those skilled in the art.

[0049] The method of the present invention may also include the step ofcoating over a previously prepared composite of PVA film and carriersubstrate. For example, the coating and drying system 10 shown in FIGS.1 and 2 may be used to apply a second multi-layer PVA film to anexisting PVA film/substrate composite. If the film/substrate compositeis wound into rolls before applying the subsequent coating, the processis called a multi-pass coating operation. If coating and dryingoperations are carried out sequentially on a machine with multiplecoating stations and drying ovens, then the process is called a tandemcoating operation. In this way, thick films may be prepared at high linespeeds without the problems associated with the removal of large amountsof solvent from a very thick wet film. Moreover, the practice ofmulti-pass or tandem coating also has the advantage of minimizing otherartifacts such as streak severity, mottle severity, and overall filmnonuniformity.

[0050] The practice of tandem coating or multi-pass coating requiressome minimal level of adhesion between the first-pass film and thecarrier substrate. In some cases, film/substrate composites having pooradhesion are observed to delaminate after application of a second orthird wet coating in a multi-pass operation. These delaminationartifacts are sometimes observed in multi-pass operations where thecarrier substrate is untreated PET. To avoid delamination defects,adhesion must be greater than about 0.3 N/m between the first-passpolyvinyl alcohol film and the carrier substrate. This level of adhesionmay be attained by a variety of web treatments including various subbinglayers and various electronic discharge treatments. However, excessiveadhesion between the applied film and substrate is also undesirablesince the film may be damaged during subsequent peeling operations. Inparticular, film/substrate composites having an adhesive force ofgreater than 250 N/m have been found to peel poorly. Films peeled fromsuch excessively, well-adhered composites exhibit defects due to tearingof the film and/or due to cohesive failure within the film. In apreferred embodiment of the present invention, the carrier substrate hasa subbing layer to improve film adhesion for tandem coating operationsor for separate off-line, multi-pass operations. In a preferredembodiment, the adhesion is less than about 250 N/m. Most preferably,the adhesion between polyvinyl alcohol film and the carrier substrate isbetween 0.5 and 25 N/m.

[0051] The method of the present invention is suitable for applicationof resin coatings to a variety of substrates such as polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), cellulose acetate,polycarbonate, polystyrene, and other polymeric films. Additionalsubstrates may include paper, laminates of paper and polymeric films,glass, cloth, aluminum and other metal supports. In some cases,substrates may be pretreated with subbing layers or electrical dischargedevices. Substrates may also be pretreated with functional layerscontaining various binders and addenda.

[0052] The prior art method of casting resin films is illustrated inFIG. 8. As shown in FIG. 8, a viscous polymeric dope is deliveredthrough a feed line 200 to an extrusion hopper 202 from a pressurizedtank 204 by a pump 206. The dope is cast onto a highly polished metaldrum 208 located within a first drying section 210 of the drying oven212. The cast film 214 is allowed to partially dry on the moving drum208 and is then peeled from the drum 208. The cast film 214 is thenconveyed to a final drying section 216 to remove the remaining solvent.The final dried film 218 is then wound into rolls at a wind-up station220. The prior art cast film typically has a thickness in the range offrom to 200 μm.

[0053] Coating methods are distinguished from casting methods by theprocess steps necessary for each technology. These process steps in turnaffect a number of tangibles, such as fluid viscosity, converting aids,substrates, and hardware that are unique to each method. In general,coating methods involve application of dilute low viscosity liquids tothin flexible substrates, evaporating the solvent in a drying oven, andwinding the dried film/substrate composite into rolls. In contrast,casting methods involve applying a concentrated viscous dope to a highlypolished metal drum or band, partially drying the wet film on the metalsubstrate, stripping the partially dried film from the substrate,removing additional solvent from the partially dried film in a dryingoven, and winding the dried film into rolls. In terms of viscosity,coating methods require very low viscosity liquids of less than 5,000cp. In the practice of the method of the present invention the viscosityof the coated liquids will generally be less than 2000 cp and most oftenless than 1500 cp. Moreover, in the method of the present invention theviscosity of the lowermost layer is preferred to be less than 200 cp.and most preferably less than 100 cp. for high speed coatingapplication. In contrast, casting methods require highly concentrateddopes with viscosity on the order of 10,000-100,000 cp for practicaloperating speeds. In terms of converting aids, coating methods generallyrequire surfactants as converting aids to control flow after coatingartifacts such as mottle, repellencies, orange peel, and edge withdraw.In contrast, casting methods do not require surfactants. Instead,converting aids are only used to assist in the stripping operation incasting methods. In terms of substrates, coating methods generallyutilize thin (10-250 μm) flexible supports. In contrast, casting methodsemploy thick (1-100 mm), continuous, highly polished metal drums orrigid bands. As a result of these differences in process steps, thehardware used in coating is conspicuously different from those used incasting as can be seen by a comparison of the schematics shown in FIGS.1 and 8, respectively.

[0054] The advantages of the present invention are demonstrated by thefollowing practical examples given below. In these examples, thepolyvinyl alcohol was the fully hydrolyzed type (greater than 98.5%saponified) with a weight average molecular weight of 98,000 daltons.

EXAMPLE 1

[0055] This example describes the single pass formation of a relativelythin PVA film on an untreated support. The coating apparatus 16illustrated in FIG. 1 was used to apply four liquid layers to a movingsubstrate 12, 170 of untreated polyethylene terephthalate (PET) to forma single layer film as illustrated earlier in FIG. 6. The substratespeed was 25 cm/s. All coating fluids were comprised of polyvinylalcohol dissolved in a solvent of 95:5 water: ethanol where the ratio isby weight. The lowermost layer 162 had a viscosity of 45 cp. and a wetthickness of 10 μm on the moving substrate 170. The second 164 and third166 layers each had a viscosity of 620 cp. and had a combined final wetthickness of 135 μm on the moving substrate 170. The uppermost layer 168had a viscosity of 185 cp. and a wet thickness of 10 μm on the movingsubstrate 170. The uppermost layer 168 also contained a surfactant(polyoxyethylene (10) isooctylphenyl ether) at a weight percent of0.10%. Coatings were applied at a temperature of 40° C. The gap betweenthe coating lip 136 and the moving substrate 12 (see FIG. 3) was 200 μm.The pressure differential across the coating bead 146 was adjustedbetween 0-10 cm of water to establish a uniform coating. The temperaturein the drying sections 66, 68, 70 was 25° C. The temperature in thedrying sections 72, 74 was 50° C. The temperature in the drying sections76, 78, 80 was 95° C. The temperature in the drying section 82 was 25°C. The composite of PVA film and PET substrate was wound into rolls.When peeled from the untreated PET substrate, the final dry film had athickness of 12 microns. The peeled PVA film had a good appearance, wassmooth, was free from wrinkles and cockle artifacts, and had an in-planeretardation of less than 1.0 nm. Properties of this PVA film aresummarized in Table I.

EXAMPLE 2

[0056] This example describes the single pass formation of a relativelythick PVA film on an untreated support. The conditions were identical tothose described in Example 1 except that the combined wet thickness ofthe second and third layers 164, 166 was increased to 290 μm. Thecomposite of PVA film and PET substrate was wound into rolls. Whenpeeled from the subbed PET substrate, the final dry film had a thicknessof 24 μm. The peeled PVA film had a good appearance, was smooth, wasfree from wrinkles and cockle artifacts, and had an in-plane retardationof less than 1.0 nm. Properties of this PVA film are summarized in Table1.

EXAMPLE 3

[0057] This example describes the single pass formation of relativelythin PVA film on a subbed support. The conditions were identical tothose described in Example 1, except that the PET support was pretreatedwith a subbing layer of poly(acrylonitrile-co-vinylidenechloride-co-acrylic acid) having a dry laydown of 100 mg/sq-m. Thecomposite of PVA film, subbing layer, and PET substrate was wound intorolls. When peeled from the subbed PET substrate, the final dry film hada thickness of 12 microns. The peeled PVA film had a good appearance,was smooth, was free from wrinkles and cockle artifacts, and had anin-plane retardation of less than 1.0 nm. Properties of this PVA filmare summarized in Table I.

EXAMPLE 4

[0058] This example describes the formation of a relatively thick PVAfilm on a subbed support using a two-pass coating operation. Theconditions were identical to those described in Example 3, except thatthe substrate was comprised of a composite of the PVA film, subbinglayer, and PET support formed in Example 3. In addition, the combinedwet thickness of the second and third layers was increased to 445microns. The composite of PVA film, subbing layer, and PET substrate waswound into rolls. When peeled from the subbed PET substrate, the finaldry film had a thickness of 48 microns. The peeled PVA film had a goodappearance, was smooth, was free from wrinkles and cockle artifacts, andhad an in-plane retardation of less than 1.0 nm. Properties of this PVAfilm are summarized in Table I.

EXAMPLE 5

[0059] This example describes the formation of a thick PVA film on asubbed support using a three-pass coating operation. The conditions wereidentical to those described in Example 2 except that the PET supportwas pretreated with a subbing layer of poly(acrylonitrile-co-vinylidenechloride-co-acrylic acid) having a dry laydown of 100 mg/sq-m. Thecomposite of PVA film, subbing layer, and PET substrate was wound intorolls. The wound composite was then over-coated with the combined wetthickness of the second and third layers at 290 μm. The composite of PVAfilm, subbing layer, and PET substrate was wound into rolls. A third andfinal coating was applied to the composite. The final dry film had athickness of 72 μm. The peeled PVA film had a good appearance, wassmooth, was free from wrinkles and cockle artifacts, and had an in-planeretardation of less than 1.0 nm. Properties of this PVA film aresummarized in Table I.

COMPARATIVE EXAMPLE 1

[0060] This example describes defects formed in a PVA film as a resultof poor drying conditions. The conditions for Comparative Example 1 wereidentical to those described in Example 3 except that the dryingconditions were adjusted such that the first three drying zones 66, 68,70 were increased to a temperature of 50° C. When peeled from the subbedPET substrate, the final dry film had a thickness of 12 microns. Thepeeled PVA film was of unacceptable quality due to a reticulationpattern in the film.

COMPARATIVE EXAMPLE 2

[0061] This example describes defects formed as a result of poor dryingconditions. The conditions for Comparative Example 2 were identical tothose described in Example 3 except that the drying conditions wereadjusted such that the first three drying zones 66, 68, 70 wereincreased to a temperature of 95° C. When peeled from the subbed PETsubstrate, the final dry film had a thickness of 12 microns. The peeledPVA film was of unacceptable quality due to a reticulation pattern inthe film as well as to blister artifacts.

COMPARATIVE EXAMPLE 3

[0062] This example describes defects in a two-pass coating operationcaused by poor adhesion to the support. The conditions for ComparativeExample 3 were identical to those described in Example 4 except that theinitial substrate was untreated PET support. Although application of thefirst coating produced a high quality PVA film having a dry thickness of12 μm, application of a second coating resulted in unacceptableblistering and delamination of the PVA from the PET support.

COMPARATIVE EXAMPLE 4

[0063] This example describes the optical properties of a film formed byprior art casting methods. A PVA film is prepared by the casting method.The apparatus 210 illustrated in FIG. 8 was used to apply a single layerto a highly polished metal drum. The speed of the metal substrate was7.5 cm/s. The casting fluid was comprised of polyvinyl alcohol dissolvedin water. The PVA casting solution had a viscosity of 30,000 cp. Thecast film was applied at a temperature of 82° C., partially dried on themoving drum, peeled from the drum, dried further, and wound into rolls.The final PVA film had a thickness of 48 μm. This film exhibited aslight cockle and had an in-plane retardation of 36 nm. Properties ofthis PVA film are summarized in Table I. TABLE I Exam- Thick- Ad- Coc-ple Support ness Re Trans Haze Ra hesion kle 1 PET 12 μn 0.50 93.1% 0.3%1.0 0.3 N/m no nm nm 2 PET 24 0.80 93.1 0.3 0.7 0.3 no 3 Sub 12 0.0493.1 0.3 1.1 4.0 no PET 4 Sub 48 0.97 93.1 0.4 0.7 7.0 no PET 5 Sub 720.25 93.1 0.3 0.9 8.0 no PET Prior Art Comp 4 None 48 36.12 92.8 0.8 0.8NA yes

[0064] The following tests were used to determine the film propertiesgiven in Table I.

[0065] Thickness. Thickness of the final peeled film was measured inmicrons using a Model EG-225 gauge from the Ono Sokki Company.

[0066] Retardation. In-plane retardation (Re) of peeled films weredetermined in nanometers (nm) using a Woollam M-2000V SpectroscopicEllipsometer at wavelengths from 370 to 1000 nm. In-plane retardationvalues in Table I are computed for measurements taken at 590 nm. Inplane retardation is defined by the formula:

R _(e) =|n _(x) −n _(y) |×d

[0067] where R_(e) is the in-plane retardation at 590 nm, n_(x) is theindex of refraction of the peeled film in the slow axis direction, n_(y)is the index of refraction of the peeled film in the fast axisdirection, and d is the thickness of the peeled film in nanometers (nm).Thus, R_(e) is the absolute value of the difference in birefringencebetween the slow axis direction and the fast axis direction in the planeof the peeled film multiplied by the thickness of the film.

[0068] Transmittance and Haze. Total transmittance (Trans) and haze aremeasured using the Haze-Gard Plus (Model HB-4725) from BYK-Gardner.Total transmittance is all the light energy transmitted through the filmas absorbed on an integrating sphere. Transmitted haze is all lightenergy scattered beyond 2.5° as absorbed on an integrating sphere.

[0069] Surface Roughness. Average surface roughness (Ra) was determinedin nanometers (nm) by scanning probe microscopy using TappingMode™Atomic Force Microscopy. (Model D300 from Digital Instruments)

[0070] Adhesion. The adhesive strength of the coated samples wasmeasured in Newtons per meter (N/m) using a modified 180° peel test withan Instron 1122 Tensile Tester with a 500 gram load cell. First, 0.0254m (one inch) wide strips of the coated sample were prepared.Delamination of the coating at one end was initiated using a piece of 3MMagic Tape. An additional piece of tape was then attached to thedelaminated part of the coating and served as the gripping point fortesting. The extending tape was long enough to extend beyond the supportsuch that the Instron grips did not interfere with the testing. Thesample was then mounted into the Instron 1122 Tensile Tester with thesubstrate clamped in the upper grip and the coating/tape assemblyclamped in the bottom grip. The average force (in units of Newtons)required to peel the coating off the substrate at a 180° angle at speedof 2 inches/min (50.8 mm/min) was recorded. Using this force value, theadhesive strength in units of N/m was calculated using the equation:

S _(A) =F _(p)(1−cos θ)/w

[0071] wherein S_(A) is the adhesive strength, F_(p) is the peel force,θ is the angle of peel (180°), and w is the width of the sample (0.0254m).

[0072] Residual Solvent A qualitative assessment of residual solventsremaining in a dried film is done by first peeling the film from thecarrier substrate, weighing the peeled film, incubating the film in anoven at 100° C. for 16 hours, and finally weighing the incubated film.Residual solvent is expressed as percentage of the weight differencedivided by the post-incubation weight.

[0073] From the foregoing, it will be seen that this invention is onewell adapted to obtain all of the ends and objects hereinabove set forthtogether with other advantages which are apparent and which are inherentto the apparatus.

[0074] It will be understood that certain features and sub-combinationsare of utility and may be employed with reference to other features andsub-combinations. This is contemplated by and is within the scope of theclaims.

[0075] As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth and shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense. PARTS LIST: 10coating and drying system 12 moving substrate/web 14 dryer 16 coatingapparatus 18 unwinding station 20 back-up roller 22 coated web 24 dryfilm 26 wind up station 28 coating supply vessel 30 coating supplyvessel 32 coating supply vessel 34 coating supply vessel 36 pumps 38pumps 40 pumps 42 pumps 44 conduits 46 conduits 48 conduits 50 conduits52 discharge device 54 polar charge assist device 56 opposing rollers 58opposing rollers 60 polycarbonate film 62 winding station 64 windingstation 66 diying section 68 drying section 70 drying section 72 diyingsection 74 drying section 76 drying section 78 dtying section 80 dryingsection 82 drying section 92 front section 94 second section 96 thirdsection 98 fourth section 100 back plate 102 inlet 104 metering slot 106pump 108 lower most layer 110 inlet 112 2nd metering slot 114 pump 116layer 118 inlet 120 metering slot 122 pump 124 form layer 126 inlet 128metering slot 130 pump 132 layer 134 incline slide surface 136 coatinglip 138 2nd incline slide surface 140 3rd incline slide surface 142 4thincline slide surface 144 back land surface 146 coating bead 150polycarbonate film 152 carrier substrate 154 carrier substrate 156subbing layer 158 polycarbonate film 160 multiple layer film 162 lowermost layer 164 intermediate layers 166 intermediate layers 168 uppermost layer 170 carrier support 172 composite film 174 lower most layer176 intermediate layers 178 intermediate layers 180 upper most layers182 carrier substrate 184 subbing layer 200 feed line 202 extrusionhopper 204 pressurized tank 206 pump 208 metal drum 210 drying section212 drying oven 214 cast film 216 final drying section 218 final driedfilm 220 wind-up station

What is claimed is:
 1. A coating method for forming a polyvinyl alcoholfilm comprising the steps of: (a) applying a liquid polyvinylalcohol/solvent mixture onto a moving, discontinuous carrier substrate;and (b) drying the liquid polyvinyl alcohol/solvent mixture tosubstantially remove the solvent yielding a composite of a polyvinylalcohol film adhered to the discontinuous carrier substrate, thepolyvinyl alcohol film being releasably adhered to the discontinuouscarrier substrate thereby allowing the polyvinyl alcohol film to bepeeled from the discontinuous carrier substrate.
 2. A coating method asrecited in claim 1 wherein: the liquid polyvinyl alcohol/solvent mixtureis applied using slide bead coating die with a multi-layer compositebeing formed on a slide surface thereof.
 3. A coating method as recitedin claim 2 wherein: the viscosity of each liquid layer of themulti-layer composite is less than 5000 cp.
 4. A coating method asrecited in claim 1 wherein: the carrier substrate is polyethylenephthalate.
 5. A coating method as recited in claim 1 wherein: thecarrier substrate has a subbing layer applied to the coated surface. 6.A coating method as recited in claim 2 wherein: an uppermost layer ofthe multi-layer composite contains a surfactant.
 7. A coating method asrecited in claim 1 wherein: the first drying section is operated at atemperature of less than 50° C.
 8. A coating method as recited in claim1 further comprising the step of: winding the composite into at leastone roll before the polyvinyl alcohol sheet is peeled from thediscontinuous carrier substrate.
 9. A coating method as recited in claim1 further comprising the steps of: (a) separating the polyvinyl alcoholfilm from the carrier substrate immediately after the drying step; and(b) winding the polyvinyl alcohol film into at least one roll.
 10. Acoating method as recited in claim 8 further comprising the step of: (a)unwinding at least a portion of the at least one roll of the composite;and (b) separating the polyvinyl alcohol film from the carriersubstrate.
 11. A coating method as recited in claim 1 wherein: thepolyvinyl alcohol film is adhered to the carrier substrate with anadhesive strength of less than about 250 N/m.
 12. A coating method asrecited in claim 9 further comprising the step of: reducing residualsolvent in the polyvinyl alcohol film to less than 10% by weight priorto the separating step.
 13. A coating method as recited in claim 10further comprising the step of: reducing residual solvent in thepolyvinyl alcohol film to less than 10% by weight prior to theseparating step.
 14. A coating method as recited in claim 8 furthercomprising the step of: delivering the composite to a user of thepolyvinyl alcohol film, the carrier substrate acting as a protectivesupport for the polyvinyl alcohol film prior to the polyvinyl alcoholfilm being separated from the substrate carrier.
 15. A coating method asrecited in claim 1 further comprising the step of: including aplasticizer in the liquid polyvinyl alcohol/solvent mixture.
 16. Acoating method as recited in claim 1 wherein: the polyvinyl alcohol filmhas an in-plane retardation of less than 35 nm.
 17. A coating method asrecited in claim 1 wherein: the polyvinyl alcohol film has an in-planeretardation of less than 10 nm.
 18. A coating method as recited in claim1 wherein: the polyvinyl alcohol film has an in-plane retardation ofless than 1.0 nm.
 19. A coating method as recited in claim 1 furthercomprising the step of: applying at least one additional polyvinylalcohol layer to the composite after the drying step.
 20. A coatingmethod as recited in claim 1 wherein: the polyvinyl alcohol film has athickness in the range of 1 to 500 μm.
 21. A composite film comprising:a PVA film coated on a discontinuous carrier substrate, the PVA filmhaving a thickness in the range of from about 1 to about 500 μm, the PVAfilm having an in-plane retardation that is less than 35 nm, thepolyvinyl alcohol film being adhered to the carrier substrate with anadhesive strength of less than about 250 N/m.
 22. A composite film asrecited in claim 21 wherein: the PVA film has an in-plane retardationthat is less than 10 nm.
 23. A composite film as recited in claim 21wherein: the PVA film has an in-plane retardation that is less than 1.0nm.
 24. A composite film as recited in claim 21 wherein: the polyvinylalcohol film is adhered to the carrier substrate with an adhesivestrength of at least about 0.3 N/m.
 25. A composite film as recited inclaim 21 wherein: the PVA film is peelable from the carrier substrate.26. A composite film as recited in claim 21 wherein: the PVA film is amulti-layer composite.
 27. A composite film as recited in claim 26wherein: at least a top layer of the multi-layer composite includes asurfactant therein.
 28. A composite film as recited in claim 21 wherein:a plasticizer is incorporated in the polyvinyl alcohol film.
 29. Apolyvinyl alcohol film made by the method of claim 1 wherein: thein-plane retardation is less than 35 nm.
 30. A polyvinyl alcohol filmcomprising: a layer of polyvinyl alcohol formed by a coating operation,the polyvinyl alcohol film having a thickness in the range of from about1 to about 500 μm, the polyvinyl alcohol film having an in-planeretardation that is less than 35 nm.
 31. A polyvinyl alcohol film asrecited in claim 30 further comprising: a plasticizer incorporated inthe polyvinyl alcohol film.
 32. A polyvinyl alcohol film as recited inclaim 30 wherein: the polyvinyl alcohol film having an in-planeretardation that is less than 10 nm.
 33. A polyvinyl alcohol film asrecited in claim 30 wherein: the polyvinyl alcohol film having anin-plane retardation that is less than 1.0 nm.
 34. A coating method asrecited in claim 1 further comprising the step of: using the polyvinylalcohol film to form a light polarizer.
 35. A display device including apolyvinyl alcohol film therein made by the method of claim
 1. 36. Apolyvinyl alcohol film comprising: a layer of polyvinyl alcohol formedby a coating operation, the polyvinyl alcohol film having an in-planeretardation that is less than about 35 nm.
 37. A polyvinyl alcohol filmas recited in claim 36 wherein: the polyvinyl alcohol film having anin-plane retardation that is less than 10 nm.
 38. A polyvinyl alcoholfilm as recited in claim 36 wherein: the polyvinyl alcohol film havingan in-plane retardation that is less than 1.0 nm.
 39. A composite filmas recited in claim 26 wherein: only a top layer of the multi-layercomposite includes a surfactant therein.
 40. A composite film as recitedin claim 26 wherein: at least a top layer of the multi-layer compositeincludes a fluorinated surfactant therein.
 41. An electronic displaydevice having view screen comprising: a polarizing film or compensationfilm prepared from a polyvinyl alcohol film having an in-planeretardation that is less than about 10 nm.
 42. An electronic displaydevice as recited in claim 41 wherein: the polyvinyl alcohol film has anin-plane retardation that is less than about 5 nm.
 43. A polyvinylalcohol film comprising: a coated layer of polyvinyl alcohol having anin-plane retardation that is less than about 10 nm.
 44. A coating methodas recited in claim 7 wherein: the drying step is initially performed ata temperature in the range of from about 5° C. to less than 50° C.
 45. Acoating method as recited in claim 7 wherein: the drying step isinitially performed at a temperature in the range of from about 10° C.to about 40° C.
 46. An electronic display device as recited in claim 42wherein: the polyvinyl alcohol film has a light transmittance of atleast about 85 percent and a haze value of less than about 1.0 percent.47. A polyvinyl alcohol film as recited in claim 43 wherein: the coatedlayer of polyvinyl alcohol has a light transmittance of at least about85 percent and a haze value of less than about 1.0 percent.
 48. Acoating method as recited in claim 1 wherein: the optical resin film hasa light transmittance of at least about 85 percent and a haze value ofless than about 1.0 percent.
 49. A coating method as recited in claim 1wherein: the optical resin film has an average surface roughness of lessthan about 100 nm.
 50. A coating method as recited in claim 1 wherein:the optical resin film has an average surface roughness of less thanabout 50 nm.
 51. A coating method as recited in claim 1 wherein: theoptical resin film has an average surface roughness of not more thanabout 1 nm.